I like the idea but it sounds like you already answered your question w.r.t. Russian defense. We don’t have those units, but here are a couple of comments…
@Warwick:
My biggest concern was adding attrition style kills (armored cars cost 3 IPP same as INF) to a blitzing stack so I included a caveat that they cannot be taken as casualties until the end of combat.
I get it - saving the med armor casualties for last makes blitzing significantly more powerful than it already is. I like to have at least a somewhat realistic basis when adding rules (helps me remember them). For this one, I would say that the support vehicles are slower than tanks, so end up behind them by the time they get to a battle. It would be awesome 8-) if that were true in real life. I’m not familiar with those units, though, so can’t say.
@Warwick:
2 Medium tanks to blitz with a 6 unit force
This seems pretty OP. What about limiting med tanks to 2 support vehicles and light tanks to 1 support vehicle. If that’s still too much, then limit to 1 support per med tank and 0 per light tank. To see which provides better balance would require some trial runs or an analysis of the 36 and 39 setups for Germany and Russia.